The present invention relates to a sintered oxide compact target for use in sputtering comprising indium (In), gallium (Ga), zinc (Zn), oxygen (O) and unavoidable impurities (generally referred to as “IGZO”; whereby the ensuing explanation will be provided by referring to the term “IGZO” as needed) and its production method.
Generally, a thin film transistor known as TFT (Thin Film Transistor) is formed from a three-terminal device including a gate terminal, a source terminal, and a drain terminal. With this kind of device, a semiconductor thin film formed on a substrate is used as a channel layer in which electrons or positive holes are moved, and voltage is applied to the gate terminal in order to control the current flowing in the channel layer, whereby provided is a function for switching the current that is flowing between the source terminal and the drain terminal. The device that has been most widely used in recent years is the type that uses a polycrystalline silicon film or an amorphous silicon film as the channel layer.
Nevertheless, since a silicon series material (polycrystalline silicon or amorphous silicon) absorbs light in a visual light range, there is a problem in that the thin film transistor will malfunction due to a carrier caused by the optical incidence. Although a light shielding layer formed of metal or the like is provided as a preventive measure, there is a problem in that the aperture ratio will decrease. Also, higher brightness of the backlight is required in order to maintain the screen brightness, and there are drawbacks such as the increase of power consumption.
Moreover, even with the deposition of amorphous silicon, which is known to be producible with a lower temperature than polycrystalline silicon in the preparation of the foregoing silicon series materials, a high temperature of approximately 200° C. or higher is required. Accordingly, with this kind of temperature, since it is not possible to use a polymer film having the advantages of being inexpensive, lightweight and flexible as the base material, there is a problem in that the range of options for the substrate material is limited. Further, there are drawbacks in terms of productivity since the process of producing devices at high temperatures requires high energy-cost and much time for the heating process.
In light of the above, a thin film transistor using a transparent oxide semiconductor in substitute for a silicon material is being developed in recent years. A typical material is the In—Ga—Zn—O (IGZO) series material. Proposals have been made for applying this material for use in a field-effect transistor since it is possible to obtain amorphous oxide in which the electronic carrier concentration is less than 1018/cm3 (refer to Patent Document 1).
In addition, various proposals have been made for using the oxide of this system in a field-effect transistor (refer to Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, Patent Document 7, Patent Document 8 and Patent Document 9).
Although Patent Document 1 suggests that the sputtering method is optimal for the deposition of amorphous oxide, Examples 1 to 12 of Patent Document 1 only show cases of performing deposition based on the pulse laser deposition method (PLD method), and only one case performs radio frequency (RF) sputtering. Similarly, Patent Documents 2 to 9 just disclose the characteristics of a field-effect transistor or describe performing reactive epitaxial method or the pulse laser deposition method as the deposition method, and none of the foregoing Patent Documents suggest performing direct current (DC) sputtering with a high deposition rate as the sputtering method.
The direct current (DC) sputtering method requires a target, but an In—Ga—Zn—O (IGZO) series oxide target is not easily manufactured.
The reason for this is that the components are a multicomponent series, and the In—Ga—Zn—O (IGZO) series oxide target entails numerous problems; specifically, it is affected by the characteristics and condition of the powder since it is produced by mixing the respective oxide powders, the characteristics of the sintered compact will differ depending on the sintering conditions, the conductivity may be lost depending on the sintering conditions and component composition, and nodules and abnormal discharge may occur during the sputtering process depending on the characteristics and condition of the target.
In light of the above, the Applicant has previously proposed an invention for inhibiting the generation of nodules and abnormal discharge during the sputtering process. This invention is an improvement of the foregoing inventions.
[Patent Document 1] WO2005/088726A1
[Patent Document 2] Japanese Patent Laid-Open Publication No. 2004-103957
[Patent Document 3] Japanese Patent Laid-Open Publication No. 2006-165527
[Patent Document 4] Japanese Patent Laid-Open Publication No. 2006-165528
[Patent Document 5] Japanese Patent Laid-Open Publication No. 2006-165529
[Patent Document 6] Japanese Patent Laid-Open Publication No. 2006-165530
[Patent Document 7] Japanese Patent Laid-Open Publication No. 2006-165532
[Patent Document 8] Japanese Patent Laid-Open Publication No. 2006-173580
[Patent Document 9] Japanese Patent Laid-Open Publication No. 2006-186319
[Patent Document 10] Japanese Patent Application No. 2007-336398